In recent years, the spread of magnetic recording media has been remarkable. Magnetic recording media have been used in one form or another in almost all homes, such as in the forms of audio magnetic tape cassettes and video magnetic tape cassettes. Audio cassettes have not only been used in stationary type stereo reproducing apparatus and radio cassette recorders, but have also been widely used for stereo systems in cars such as a private car, etc. The video cassettes have not only been used for stationary type video tape recording (VTR) but also portable VTR by which video imaging can be conducted outdoors. Moreover, in recent years, subminiature incorporated-camera type VTR called "8 mm video" has been studied.
Magnetic tape cassettes ordinarily used hitherto indoor have now been used outdoors, as described above, because of their easy handling and commercial availability. However, it is clear that conditions of use outdoors are typically more severe than those of use indoors. In the case of use or storage indoors, it is sufficient to consider a temperaure range of from 0.degree. C. to 50.degree. C. or so. However, in case of using outdoors, it is more typical that use or storage may encounter a temperature range of from -40.degree. C. to 120.degree. C. A typical example of using outdoors is in stereo systems in cars. According to a standard by Corporate Juridical Person: Jidoshagijutsukai (JASO M317-75, standars inspection of plastic moldings for cars), the 1st grade condition for a temperature resisting test of car parts covers the range of from -40.degree. C. to 120.degree. C. Such severe conditions for storage temperature required for such cases are too severe for the prior magnetic tape cassettes and storage cases which were designated so as to be used indoors.
Hitherto, magnetic tape cassettes and storage cases made of various materials are proposed, for example, in Utility Model Application (OPI) No. 167085/81, Utility Model Publication Nos. 12349/75 and 33539/76 and Japanese Patent Application (OPI) Nos. 41343/84, 154686/82 and 137173/83. However, their heat resisting temperature is at the most 70.degree. C. to 80.degree. C., or so. Therefore, in case that an audio cassette or the storage case therefor is left on the dashboard, the surface temperature may sometimes rise to 110.degree. C. or more by direct exposure to the sun through the glass, and, consequently, the audio cassettes or the storage case may frequently be subject to thermal deformation, whereby it becomes impossible to insert the cassette into a car stereo deck, or it becomes impossible to accommodate the cassette in the storage case.
Further, even if the audio cassette does not undergo deformation, a label, which is typically applied to the surface of it, can undergo so-called label floating, because of expansion and contraction of the audio cassette by heat, since the label has a different coefficient of expansion and contraction. If such label floating occurs, it can cause the problem that the audio cassette can not be removed after it is inserted in the car stereo deck, because the label sticks to the inside of the deck.
In the case of the video cassette, there is even more possibility of such a problem occurring, because it is composed of a larger number of parts as compared with the audio cassette. For example, a front opening part for drawing the tape in the video cassette is covered with a covering member (hereinafter referred to as the guard panel) to provide for dustproofing. In many cases, the guard panel is composed of a plate having a nearly L-shaped section in order to cover the front opening part. This shape easily warps when heat is applied thereto. If deformation such as a warp, etc., is once caused, it becomes impossible thereafter to smoothly carry out opening and closing of the guard panel. In the video cassette, the tape is drawn from the video cassette and it is wound on a magnetic drum for reproduction of recording. Therefore, when the guard panel does not function normally, physical damage or a scratch which can not be recovered is applied to the magnetic tape by the guard panel.
Thus, since audio cassettes and video cassettes have been increasingly used outdoors, high temperature durability has been required for the magnetic tape cassettes and the storage cases.
Particularly, audio cassettes for car stereos used in cars must maintain good characteristics even though subjected to particularly severe conditions. Thus, it has been required that the characteristics are stably maintained generally at a temperature of 110.degree. C. or higher.